The present invention relates to mounts and fasteners. More specifically, the present invention relates to inset panel fasteners which are particularly useful within the aircraft industry.
Many types of mounting devices have been developed for holding one or more objects to a support surface. For example, inset-type fasteners are generally anchored into a structure and include an engagement portion, such as the male or female threads of a screw, for securing objects to the structure. Inset fasteners are particularly advantageous when a strong connection between the structure and object cannot be readily obtained through use of a surface mounted structure.
Sandwich panels are used extensively in the aircraft and marine industries. These sandwich panels typically are made of fiberglass or similar material formed in a honeycomb structure. The honeycomb structure is then typically sandwiched between outer layers of aluminum panels or the like. These sandwich panels are preferred as a result of their relatively inexpensive price, lightweight and high strength. In order to anchor objects to the sandwich panel, inset panel fasteners are typically used. To anchor the inset panel fastener in place, a cavity is typically formed directly through the outer aluminum layer into the honeycomb core using a drill or the like. The inset panel fastener is then positioned within the cavity and an adhesive or other binding material is injected into the cavity to secure the fastener to the honeycomb core. Since the cavity is cylindrical, most inset panel fasteners include a cylindrical body having a central bore. The central bore typically includes female threads functioning as a fastener element. Alternatively, some inset panel fasteners include a floating fastener element in the form of a nut which also includes female threads which is floatingly positioned within the bore. Examples of inset panel fasteners including floating elements include U.S. Pat. Nos. 4,973,208 and 5,632,582. Inset panel fasteners have been manufactured from a variety of materials. For example, it has been known to manufacture an inset panel fastener of various metals including steel and titanium. Conversely, U.S. Pat. No. 4,846,612 describes a one piece inset panel fastener made from a thermoplastic.
All metal fasteners provide extremely high strength to an affixed fastener element. However, adhesives and potting materials typically do not bond to an all metal material, such as titanium, as well as to a plastic material. All metal fasteners are also heavy and expensive.
Meanwhile, inset panel fasteners made of plastic suffer from disadvantages of their own. Like metal inset panel fasteners, most plastic inset panel fasteners include a cylindrical body. The cylindrical body includes a central bore including integrally formed female threads or includes a separate female fastener element, often constructed of metal. The body further includes an opening or entrance formed at the body's top for insertion of a male fastener element to engage the female fastener element. Projecting radially from the top of the body, the inset panel fastener further includes a disk which has a diameter greater than the diameter of the body to form a cavity space around the body's for injection of an adhesive or potting material within the sandwich panel cavity.
Unfortunately, these plastic inset panel fasteners suffer from several disadvantages. Fasteners having plastic threads can often withstand the load bearing stresses imposed by an object affixed to the substrate. However, threads made of plastic are typically not acceptable as locking threads where repeated engagement and disengagement may be encountered. Locking female threads have a means of providing extra friction between itself and the male threads of a bolt. Typically, locking female threads are distorted to insure interference during engagement to male threads. This interference provides the desired “locking action” caused by a large increase in friction. In practice, this “locking action” is evident to a technician as a sudden rise in “running torque” when male threads engage locking female threads.
It is preferred that female locking threads be able to withstand fifteen (15) or more cycles of full engagement and disengagement with a male threaded element as specified in aircraft industry specification NASM 25027 which is incorporated by reference herein. Unfortunately, the telescopic rotations of the male threads against the plastic female threads of a plastic female fastener element causes the locking mechanism to wear down after only a few engagements and disengagements. Once the locking mechanism has worn down, the locking threads are no longer capable of “locking” the male threads to the female threads making unwanted disengagement an unacceptable possibility. Accordingly, inset panel fasteners having plastic threads have not be adopted in industry where a locking feature is required.
Inset panel fasteners having been constructed to include a plastic outer body and a metal inner female fastener element, commonly referred to as a nut. These composite constructions are lighter than all metal constructions. In addition, the female metal threads of the nut are capable of fifteen or more cycles of engagement and disengagement with a male fastener without eliminating the locking capabilities of locking threads. Unfortunately, these constructions are still undesirably heavier than all plastic constructions.
Thus, it would be advantageous to provide an improved inset panel fastener which included locking threads capable of fifteen cycles or more without loss of locking capabilities.
It would be an additional advantage to provide an improved panel fastener that was lightweight.
It would be still an additional advantage to provide an improved inset panel fastener that was lightweight comparable to an all plastic fastener, but provided the cyclic locking capabilities of an all metal fastener.
Furthermore, it would be still an additional advantage to provide an improved inset panel fastener that was inexpensive to manufacture.